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High Temperature Oxidation and Chlorination of FeCrAl alloys

Niklas Israelsson (Institutionen för kemi- och bioteknik, Oorganisk miljökemi)
Göteborg : Chalmers University of Technology, 2014. ISBN: 978-91-7597-093-6.- 81 s.
[Doktorsavhandling]

Abstract The constant strive for improved efficiency and lower-cost industrial processes often results in progressively higher temperatures and more aggressive environments. High- temperature corrosion is a well-known problem in biomass- and waste-fired boilers and is one of the obstacles to overcome in achieving a more sustainable society. Alkali- and chlorine- induced corrosion of chromia-forming alloys has been studied by several researchers. However, the literature is scarce on how alumina forming-alloys, e.g. FeCrAl alloys, perform in such an aggressive environment. In this thesis, the KCl-induced corrosion of FeCrAl alloys is studied through well-planned laboratory exposures, detailed analyses and corrosion tests in a full scale waste-fired power boiler. In the laboratory, the effect of adding small amounts of KCl was investigated on polished FeCrAl samples in O2 or O2 + H2O environments up to 168 hours at 600 °C. Pre-formed alumina scales were prepared on the alloy substrate through pre-oxidation at various conditions. The pre-treated samples were subsequently exposed to O2 + H2O + KCl in order to investigate their corrosion resistance. The samples were analysed using TGA, SEM/EDX, XRD, IC, AES, SIMS, BIB cross sections and STEM/EDX. In order to evaluate the validity of the findings in the laboratory studies, corrosion tests were carried out in a full-scale combined heat and power (CHP) boiler. The study showed that KCl-induced corrosion caused a rapidly growing iron-chromium-rich oxide to form in O2 and O2 + H2O environments at 600 °C. Chromate formation and alloy chlorination were found to initiate the formation of a non-protective oxide scale. Alloy chlorination was greater in O2 than in O2 + H2O resulting in a more porous scale with poor adhesion to the alloy substrate. Pre-treating the alloy prior to exposure to O2 + H2O + KCl mitigated the corrosion, since alumina, itself, is rather inert towards corrosion. However, the corrosion started locally, most likely at flaws/cracks in the alumina scale and then spread laterally until the entire surface suffered from breakaway corrosion. Similar results were obtained in the corrosion tests in the waste-fired boiler. The pre-formed alumina scale failed after only 24 hours in the boiler at both 600 and 700 °C.

Nyckelord: FeCrAl, high-temperature corrosion, KCl, H2O, pre-oxidation, kinetics



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Denna post skapades 2014-11-17. Senast ändrad 2015-03-18.
CPL Pubid: 205899

 

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Institutioner (Chalmers)

Institutionen för kemi- och bioteknik, Oorganisk miljökemi (2005-2014)

Ämnesområden

Energi
Materialvetenskap
Metallurgi och metalliska material

Chalmers infrastruktur

Examination

Datum: 2014-12-12
Tid: 13.15
Lokal: HA3-salen, Hörsalsvägen 4, Chalmers
Opponent: Professor John Nicholls, Cranfield University, UK.

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